The present invention relates to the treatment of running webs which consist of paper or the like, especially to the treatment of running webs of the type used in the tobacco processing industries. Such webs include cigarette paper, imitation cork or other types of so-called tipping paper which is used in filter tipping machines to unite plain cigarettes, cigars or cigarillos of unit length or multiple unit length with filter mouthpieces of unit length or multiple unit length. More particularly, the invention relates to improvements in apparatus for perforating and testing webs of cigarette paper or the like in or outside of tobacco processing machines.
It is already known to perforate a running web of cigarette paper or the like for the purpose of providing the wrappers of plain or filter cigarettes, cigars, cigarillos, filter rod sections or other rod-shaped smokers' products with so-called ventilating zones which admit cool atmospheric air into the column of tobacco smoke. It is believed that the admission of cool atmospheric air into hot tobacco smoke exerts a beneficial influence on the effect of nicotine and condensate upon the health of the smoker. The perforating operation can be carried out at the locus of manufacturing and winding the web or directly in the processing machine, e.g., in a filter tipping machine upstream of the station where tobacco-containing rod-shaped articles are joined with filter plugs to form therewith filter cigarettes, cigars or cigarillos of unit length or multiple unit length. The web is drawn from a reel or another suitable source of supply by one or more pairs of advancing rolls which transport the web through a perforating unit, and the thus perforated web is thereupon normally transported through a pneumatic testing or monitoring device which ascertains the permeability of the perforated web and generates signals serving to adjust the perforating unit if the detected permeability deviates from an optimum value, i.e., if the articles containing portions of the monitored web would permit excessive or insufficient quantities of atmospheric air to enter the wrappers of the articles and to mix with the column of tobacco smoke. The perforated and tested web is then converted into a reel which can be shipped to a cigarette making or like plant, or the web can be immediately converted into the wrappers of rod-shaped smokers' products.
British Pat. No. 1,588,980 discloses one form of means for perforating a running web of cigarette paper or the like. The patented perforating unit employs a set of needles or analogous mechanical perforating tools which puncture selected portions of the running web. U.S. Pat. No. 2,528,158 and British Pat. No. 1,604,467 disclose electroperforating units which employ electrodes arranged to generate heat and to thus combust selected portions of the running web. A further perforating unit is disclosed in U.S. Pat. No. 4,265,254 and in British patent application No. 2,074,493 each of which proposes to use one or more sources of laser beams. Coherent radiation which is furnished by a laser is capable of making perforations of desired size with a high degree of reproducibility so that such perforating units can ensure proper ventilation of the wrappers of cigarettes or other smokers' products in which the perforated web is put to use.
The aforementioned U.S. Pat. No. 2,528,158 further discloses pneumatic testing of the web downstream of the perforating unit. As mentioned above, the results of the test can be used to adjust the perforating unit if the pneumatically ascertained permeability of the perforated web deviates from an optimum value. For example, signals which are generated by the pneumatic testing unit can be used to regulate the width and/or frequency of pulses which are employed in the patented unit to perforate the running web. The testing device is quite accurate; however, its inertia is rather pronounced so that the adjustment of the perforating unit is delayed sufficiently to permit defective portions of the web to reach the processing machine and to cause the making of unsatisfactory articles, e.g., of cigarettes whose wrappers exhibit excessive or insufficient porosity. In fact, it can happen that the processing machine receives web portions which are devoid of any perforations. This is attributable to the aforediscussed inertia of the pneumatic testing device, i.e., the device generates signals with a pronounced delay after the defective portion of the web has advanced therebeyond. This is particularly undesirable in modern high-speed machines, such as recent types of cigarette makers or filter tipping machines, which can turn out extremely large quantities of rod-shaped articles per unit of time so that even relatively short delays in detection and/or indication of detection of improperly perforated web portions can result in the making of substantial numbers of defective articles.